Bilateral non-reflective transmission device



United States Patent O F BILATERAL NON-REFLECTIVE TRANMISSION DEVICE Takaji Kuroda and Susumu Kitazume, Tokyo, Japan, as-

signors to Nippon Electric Company, Limited, Tokyo, Japan, a corporation of Japan Filed Nov. 25, 1964, Ser. No. 413,946 Claims priority, application Japan, Dec. 4, 1963, 38/ 65,241 12 Claims. (Cl. 333-6) This invention relates to microwave equipment and more particularly to means in said equipment for eliminating the adverse effects of reflected waves. In particular, although not limited thereto, this invention relates to means of the kind to be used in a feeder of a microwave transmitter-receiver.

In a microwave transmitter-receiver, one well-known ,ethod for reducing the cost for manufacture, is to utilize a single common antenna for both transmission and reception and to use a common waveguide feeder to interconnect the common antenna with a plurality of transmitters and receivers. The impedance of such an antenna which is used for both transmission and reception is selected so as to be suitable for the wide frequency range occupied by the transmitted waves and the received waves. Such a system cannot be brought into the completely matched state for most of the frequencies contained Within the range. Therefore, the V.S.W.R. which results when the antenna is viewed from each of the points where the feeder is coupled through the individual branching filters with a plurality of transmitter-receivers is always greater than unity and is in the order of 1.05 at the minimum. Also, the V.S.W.R. seen from each of the above-mentioned coupling points to the corresponding transmitter-receiver cannot generally be reduced to unity and as a result will generally be greater than unity. Consequently, a portion of the wave transmitted from one of the transmitters is reflected at the antenna back towards the transmitter and again at the transmitter towards the antenna. Inasmuch as the transmitted wave, the reflected wave, and the secondary reflected wave interact with one another, the transmitted wave undergoes phase shift and other distortions. Likewise, the received microwave is reflected at the receiver and again at the antenna and also undergoes distortion. When the antenna is installed on a tall tower, as it is generally used in a microwave communication equipment, the feeder necessarily becomes long. As a result, the adverse eifects caused by the reflected waves become even more serious. It is already known that such adverse effects can be completely eliminated by utilizing difierent antennae for transmission and reception, and by interposing an insolator in each of the feeders for eliminating the reflected waves. This however, requires twice as many antennae as the system using a common antenna and in addition is very costly in a microwave long-distance communication system where a large number of repeater stations is necessary or where a large number of antennae is required or in a microwave over-the-horizon communication system where an antenna of large diameter and consequently of high cost is used.

An object of this invention, therefore, is to provide an improved microwave feeder apparatus.

Another object of this invention is to provide a bilateral non-reflective transmission device for eliminating the effect of the reflected waves in a feeder interconnecting a microwave transmitter-receiver with a common antenna.

The bilateral non-reflective transmission device of this invention has two or three signal transmission paths composed of waveguides. A pair of branched circuits, such as circulators, T-branches, or magic tees, couples all the corresponding ends of these signal transmission paths to 3,324,410 Patented June 6, 1967 the input-output ends of the device, respectively. One or two filters is interposed in each of at least two signal transmission paths. Either an isolator is interposed in each of or in one of the signal transmission paths or a a dummy load is attached to one of the branch circuits. In this device, the directivity of the branched circuits, the pass band of each of the filters, the relative positions of the filters with respect to the branch circuits, and the forward direction of the isolator are so arranged that two high-frequency signals of different frequency bands (which are supplied to the device in different directional senses, such as the transmit-ted and the received microwaves travelling through a feeder) are propagated through the respective particular signal transmission paths and the reflected waves of the respective highfrequency signals are absorbed by the isolator or the dummy load.

The above-mentioned and other features and objects of this invention and the means for attaining them will become more apparent and the invention itself will be best understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a first embodiment of the invention;

FIG. 2 illustrates a modification of the first embodiment in FIG. 1;

FIG. 3 is a schematic diagram of a of the invention; and

FIG. 4 is a schematic diagram of a third embodiment of the invention.

Referring to FIG. 1, the bilateral non-reflective transmission device illustrated therein is the basic form of the invention. In FIG. 1, a first and a second input-output ends are indicated by reference numerals 101 and 121. A first and a second three-port circulators and 125 are provided and respectively have a first arm 102 and 122 connected to the respective input-output ends 101 and 121. The second arms 103 and 123 and third arms 104 and 124 are angularly spaced by from the respective first arms 102 and 122. Ferromagnetic members (not shown), such as a ferrite or Y.I.G. (yttrium iron garnet) members are disposed at the respective branching points of the three arms. The change of the magnetic permeability of these members varies according to the supplied magnetic" field. The magnetic field in turn is provided by means (not shown) which supply each branching point with a magnetic field such that: the microwaves received from the first arm 102 or 122 are respectively transmitted to the second arm 103 or 123 only; the microwaves received from the second arm 103 or 123 are transmitted only to the third arm 104 and 124; and the microwaves received from the third arm 104 or 124 are transmitted only to the first arm 102 or 122. A first and a second band-pass filters 111 and 112 are respectively connected to the respective second arms 103 and 123 of .the circulators. These filters have different pass bands hi-Af and fzi Afg, respectively, which range on both sides of their respective center frequencies f and f A first isolator 113 is interposed between filter 111 and the third arm 124 of the second circulator 125. Second isolator 114 is interposed between filter 112 and the third arm 104 of circulator 105. These isolators are respectively adapted to transmit the microwaves travelling from the first filter 111 to the third arm 124 and from the second filter 112 to the third arm 104 without substantial loss and the microwaves travelling in the reversed directional sense with substantially infinite loss.

The operation of .the bilateral non-reflective transmission device of FIG. 1 will now be explained for the second embodiment case where this embodiment is to be disposed in a common feeder through which the transmitted and the received microwaves F and F (occupying the respective frequency ranges f idf and fgiAfz), respectively travel along with their reflected waves. In this case, the device is interposed in the feeder at any desired point in such a manner that the first input-output end 101 is disposed on the side nearest the transmitter-receiver and the second input-output end 121 is placed on the side nearest the common antenna. The device, through end 101 nearest the receiver-transmitter is supplied with microwave F which is to be transmitted along with the reflected wave F which occupies the same frequency range as the received microwave F The device receives at end 121 thereof (nearest the antenna) the received microwave F and the reflected wave F of the transmitted microwave F The microwave F to be transmitted is supplied to the device through the first input-output end 101 and is delivered by the first circulator 105 to the second arm 103 thereof. After passing through the first bandpass filter 111 and the first isolator 113 (which is directed in the forward sense for the microwave F this microwave is supplied .through the third arm 124 of the second circulator 125 to the first arm 122 thereof. It is then delivered through the second input-output end 121 and the feeder to the common antenna. On the other hand, the reflected wave P (of the transmitted microwave F is reflected at the common antenna and supplied back to the device through the second input-output end 121. Reflected wave F is then sent by the circulator 125 to the second arm 123 thereof. Wave F is then reflected back to circulator 125 through arm 123 by the second band-pass filter 112 whose pass band is different from the frequency band occupied by this reflected Wave F Wave F is then circulated to the third arm 124 of circulator 125, where it is supplied to and absorbed by the first isolator 113 which operates to pass signals supplied thereto by filter 111 and not in the directional sense of propagation of the reflected wave F The operation of the device is the same for the received microwave F and to the reflected wave F More particularly, the received microwave F supplied to the device through the end 121 is sent through the arm 123 of the second circulator 125 to and successively through the second band-pass filter 112, .the second isolator 114, the third arm 104 of the first circulator 105, the arm 102 of the first circulator 105, and then to the first input-output end 101. Similarly, the reflected wave F of the received microwave F enters the device through the first input-output end 101 and goes through the first circulator 105 and the second arm 103 thereof to the first band-pass filter 111 where it is reflected back through this arm 103 again. Circulator 105 then circulates this signal from arm 103 to the third arm 104 thereof, to be absorbed at the second isolator 114.

The same effect may be achieved by modifying the above-described first embodiment illustrated in FIG. 1 as follows: The second isolator 114 is omitted and the second filter 112 is directly connected to the third arm 104 of the first circulator 105. In this first modification, the reflected wave P of the received microwave F will be reflected by the first filter 111, and will then be circulated to the third arm 104 of the first circulator 105. It is then sent through the second filter 112 and the second arm 123 of the second circulator to the third arm 124 of the circulator 125 where it is absorbed by the first isolator 113. In practice, an isolator transmits on the reversed directional sense, microwave power of the order of -10 The first modification which has only one isolator is therefore inferior to the embodiment of FIG.,1 in its ability to eliminate the reflected waves.

Referring to FIG. 2, a bilateral non-reflective transmission device is illustrated therein. This device is a second modification of the first embodiment illustrated in FIG. 1. The device of FIG. 2 is formed by omitting the second isolator 114 and by replacing the first isolator 113 and the second circulator 125 of FIG. 1 with a four port circulator 201. A first arm 202 of circulator 201 is connected to the second input-output end 121; a second arm 203 is connected to the second band-pass filter 112; a third arm 204 is connected to a dummy load 206, and the fourth arm 205 is connected to the first band-pass filter 111. End 121 in turn is connected to the antenna or other utilization device generally shown as block 5. In FIG. 2, parts similar to those in FIG. 1 are designated with like numerals. It should also be noted that the four-port circulator 201 transmits a microwave supplied from one of the arms thereof to the adjacent arm in a clockwise sequence starting from the first arm 202 to the fourth arm 205 and then returning to the first arm 202. It will be apparent with the second modification that both transmitted and received microwaves F and F travel as indicated in the first embodiment. As for the reflected waves thereof, the reflected wave P of the transmitted microwave F is supplied to the device from the end 121 and is then delivered by the four-port circulator 201 to the second arm 203 thereof to be reflected back by the second band-pass filter 112. This reflected wave from filter 112 is circulated from arm 203 through the four-port circulator 201 to the arm 204 thereof, where it is absorbed by the dummy load 206. On the other hand, the reflected Wave P of the received microwave F which is supplied from the first input-output end 101 from receiver-transmitter 4 to the device is delivered through the first circulator and the second arm 103 thereof to the first band-pass filter 111 where it is reflected back to circulator 105. It is thus circulated to arm 104 thereof. It passes through the second band-pass filter 112, and is transmitted through the arm 203 of the fourport circulator which then circulates said signal to arm 204 thereof, where the dummy load 206 absorbs reflected wave F therein.

Referring to FIG. 3, there is illustrated therein a bilateral non-reflective transmission device which is a second embodiment of the invention. The device of FIG. 3 includes a first and second input-output ends 301 and 321.

A first and a second E-branch, H-branch or Y-branch (an explanation will be made hereinafter with reference to a T-branch which can be either an E-branch or an H- branch) 305 and 325 are provided. These branches have: first arms 302 and 322 connected to the respective inputoutput ends 301 and 321; second arms 303 and 323 and third arms 304 and 324. The second and third arms are symmetrical with respect to the corresponding first arms 302 and 322, respectively. A first and a second band-pass waveguide filters 311 and 312 are provided. Each has a common pass frequency band f it, which is the band occupied by the transmitted microwave F These filters are connected to the respective second arms 303 and 323 of the first and the second T-branches 302 and 322 such that each of the extension planes 306 and 326 (which would be obtained by virtually extending the walls of the waveguides on the side of the respective second arms 303 and 323 as indicated by dashed lines) can be spaced from the rods of the corresponding waveguide filter disposed nearest to the corresponding surface 306 and 326 of extension, by a distance which is approximately an integral multiple of a half of the, guide wavelength Ag of the microwave having the center frequency f of the received microwave F By such spacing the virtual surfaces 306 and 326 of extension indicated by the dashed lines act in effect as short circuiting surfaces for the received microwave F A third and a fourth band-pass waveguide filters 313 and 314 are also provided. These filters have a common pass frequency band f iAf which is the band occupied by the received microwave F These filters are connected to the respective third arms 304 and 324 of the first and second T-branches 302 and 322 such that each of the extension planes 307 and 327 obtained by virtually extending the walls of the waveguides on the side of the respective third arms 304 and 324 (as indicated by the dashed lines) can be spaced, from the rods of the corresponding waveguide filter (disposed nearest to the corresponding extension surface 307 or 327 )by such a distance which is substantially equal to an integral multiple of half a wavelength Ag; of a microwave having the center frequency i of the transmitted microwave F By such spacing, the extension surfaces 307 and 327 act in effect as short circuiting surfaces for the transmitted microwave F A first and a second isolators 315 and 316 are interposed between the first and the second filters 311 and 312 and between the third and fourth filters 313 and 314 respectively. These isolators transmit the microwaves in opposite directional senses. If the forward direction of the first isolator 315 is from the first T-branch 305 towards the second T-branch 325, the device should be dis posed in the feeder in such a manner that the first inputoutput end 301 is nearest the transmitter-receiver.

Inasmuch as the first and the second band-pass lters 311 and 312 in effect form short circuiting planes for the microwave having a center frequency f of the received microwave and other frequencies outside of the transmission band thereof (at a point spaced by a few millimeters from the rods on that side thereof to which the microwave is supplied and through points spaced from the first-mentioned point by integral multiples of the half guide wavelength Xg /Z) the received microwave F supplied from the input-output end 321 will be delivered to the third arm 324 of the second T-branch 325 by the effective short circuiting plane formed in registration with the extension plane 326 on the side of the second arm 323. The received microwave F is then transmitted to and successively through the filter 314; the isolator 316; the filter 313; to the first T-branch 305. It will then be reflected to the first arm 302 by the effective short circuiting plane 306 on the side of the second arm 303, and will be delivered through the first input-output end 301 to the feeder. On the other hand, the reflected wave P of the received microwave F supplied to the device through the end 301 is delivered by the aforementioned short circuiting plane in the first T -branch 305 to the third arm 304 and will thereafter be absorbed by the second isolator 316. The transmitted microwave F and the reflected wave F thereof are similarly reflected by the respective effective short circuiting planes formed in the first and the second T-branches 305 and 325 in register with the extension planes 307 and 327 on the side of the third arms 304 and 324. The transmitted microwave F will thus be transmitted along the path between (from end 301) the second arms 303 and 323 of the first and the second T-branches 305 and 325 to the second end 321. The reflected wave F is transmitted from the end 321 to the second arm 323 of the second T'branch 325 and it is then absorbed by the first isolator 315.

If either of the reflected waves, (reflections of either the transmitted or received microwaves) is not present in the feeder or if the reflected wave F of the received microwave F does not appear because the V.S.W.R. of the receiver is equal to unity, then the embodiment shown in FIG. 3 may be modified by removing from the device either of the third and the fourth filters 313 and 314 and the second isolator 316. It should, however, be noted that the remaining filter 313 or 314 must be placed such that the distance between each of the extension planes 307 and 327 on the side of the third arms 304- and 324 of the two-T-branches 305 and 325 and the filter rods on the side of the adjacent end can be made equal to an integral multiple of the half guide wavelength A /Z.

Finally, referring to FIG. 4, the bilateral non-reflective transmission device illustrated therein is still another embodiment of the invention. In this embodiment first and second input-output ends 401 and 421 are provided. A first and a second magic tees 403 and 423 are provided and have magnetic arms 402 and 422 connected to the input-output ends 401 and 421, respectively. Four waveguide band-pass filters 411 through 414 (Whose pass bands are all equal to the frequency band occupied either by the transmitted microwave F or by the received microwave F are connected to the electromagnetically equivalent arms 404, 405, 424, and 425 of the first and the second magic tees 403 and 423, respectively. A first and a second isolator 415 and 416 are respectively connected between the first and the third filters 411 and 413 and between the second and the fourth filters 412 and 414. The forward directions of these isolators are directed in the same sense. A third isolator 417 is connected between electric arms 406 and 426 of the first and the second magic tees 403 and 423 such that the forward directions thereof are in a reversed sense with respect to the forward direction for isolators 415 and 416. The difference between the distances from the center point 407 of the first magic tee 403 to the equivalent short circuiting planes of the first and the second filters 411 and 412 connected thereto and the diiference between distances from the center point 427 of the second magic tee 423 to the equivalent short circuiting planes of the third and the fourth filters 413 and 414 connected thereto are each equal to an odd integral multiple of a quarter guide wavelength of the microwave whose frequency is equal to the center frequency of either the transmitted or the received microwaves F and F which frequency will not pass through the filters 411 and 414. The difference between the distances between the center points 407 and 427 of the magic tees 403 and 423 (as measured along the two paths including the respective isolators 415 and 416) are equal to an integral multiple of the guide wavelength of the microwave whose frequency is equal to the center frequency of the microwave which does pass through the filters 411 through 414.

If the common pass band of the filters 411 through 414 is the frequency band occupied by the received microwave F and if the forward direction of the isolators 415 and 416 is from the end 421 to the end 401, the device of FIG. 3 should be interposed in the feeder such that the end 401 is nearest the transmitter-receiver. A magic tee will transmit microwaves received through the magnetic and the electric arms only to both of the electro-magnetically equivalent arms in the same phase and in the opposite phases, respectively; and microwaves received simultaneously through the electromagnetically equivalent arms only to the magnetic arm if the microwaves are in phase, and only to the electric arm if they are in phase opposition. Therefore, the transmitted microwave F supplied to the device through the end 401 will be delivered in phase to the electromagnetically equivalent arms 404 and 405 of the first magic tee 403. These separate microwaves will be reflected by the equivalent short circuiting planes (formed by the first and the second filters 411 and 412, respectively) back towards the center point 407 of the magic tee 403. These reflected microwaves reach point 407 in phase opposition because of the diffe ence of a half guide wavelength Ag /Z existing between the total paths for these microwaves. As a result the transmitted microwave F will then deliver to the electric arm 406. This microwave F is then sent through the third isolator 417 and the electric arm 426 to the second magic tee 423 and thence to the electromagnetically equivalent arms 424 and 425 in opposite phases. The thus separated microwaves are then reflected by the equivalent short circuiting planes (formed by the third and the fourth filters 413 and 414, respectively) in phase back towards the center point 427 of the second magic tee 423 where they are sent in turn to the magnetic arm 422. In this manner, the transmitted microwave F is sent to the second input-output end 421. The reflected wave P of the transmitted microwave F which reaches the device through the second end 421 is delivered to the second magic tee 423 through the magnetic arm 422 and through a similar path as mentioned above 7 to the electric arm 426 thereof to be absorbed by the third isolator 417. On the other hand, the received microwave F supplied to the second magic tee through the end 421 is sent in phase to the electromagnetically equivalent arms 424 and 425 thereof and then through two paths. The

first path includes the filter 413, the first isolator 415,

and the first filter 411. The other path includes the filter 414, the second isolator 416, and the filter 412. The wave F in both paths is then supplied to the center point 407 of the first magic tee 403. These microwaves are in phase at the center point 407 because their paths are of equal length (or differ by an integral multiple of a guide Wavelength kg As a result the received microwave F appears at the magnetic arm 4G2 and is sent out through the first end 401. It will now be apparent that the reflected wave F of the received microwave F will be absorbed by the first and the second isolators 415 and 416.

If one of the reflected waves for example, the wave P of the received microwave F is not present in the feeder then the third embodiment may be simplified by removing from the device shown in FIG. 4 either filters 411 and 412 or filters 412 and 413 together with isolators 415 and 416.

As explained hereinabove, it is possible with a bilateral non-reflective transmission device of the invention interposed in a feeder, to deliver the transmitted microwave to a common antenna and to deliver the microwave received by the common antenna to the receiver while simultane ously eliminating reflected waves which would introduce distortions into the transmitted and the received microwaves. Inasmuch as the insertion loss of the bilateral nonreflective transmission device is only of the order of 1.0 db, it may be neglected if one considers the distortions that are avoided. Incidentally, use of a plurality of devices of the invention in a feeder instead of only one will make it possible to enhance the technical merits of the invention and will enable the use of very long feeders. Thus, this invention will help remove the restrictions which are normally encountered when designing the microwave circuit.

Although in the illustrated embodiments one or a plurality of devices of the invention was used for only one transmitter-receiver it will be recognized that the device of this invention can be used when a plurality of transmitter-receivers are to be used. In this case, the pass bands of the band-pass filters should be adapted to the resultant frequency bands occupied by the transmitted microwaves and the received waves respectively. Also, the band-pass filters mentioned in the above embodiments may be bandrejection, high-pass, or low-pass filters, for permitting that microwave to pass through, which the replaced band-pass filters have caused to pass. Furthermore, the two branched circuits used in any one of the above embodiments need not be of the same type but may be of different types. For

example, one may be a circulator while the other may be a T-branch.

A bilateral non-reflective transmission device of the invention is not only applicable, as heretofore explained, to a feeder connecting a common antenna to one or a plurality of transmitter-receivers, but is also applicable to any transmission path which simultaneously propagates two high-frequency signals of different frequency bands in opposite senses, and wherein reflected waves might be produced to adversely affect the transmission characteristics 8 different frequency bands in opposite directions comprisfirst input-output means having an inherent impedance mismatch for said other signal and passing said one and other signals and reflecting a portion of said other signal,

second input-output means having an inherent impedance mismatch for said one signal and passing said one and other signals and reflecting a portion of said one signal,

a first path transmitting said one signal in a given direction from said first input-output means to said second input-output means to said second input-output means,

a second path transmitting said other signal in a direction opposite to said given direction from said second input-output means to said first input-output means,

first circuit means interconnecting said first inputoutput means and adjacent ends of said first and second paths for passing said one signal and reflected other signal portion in said given direction and said other signal in said opposite direction,

second circuit means interconnecting said second inputoutput means and adjacent opposite ends of said first and second paths for passing said one signal in said given direction and said other signal and reflected one signal portion in said opposite direction,

and means coupled to said first and second circuit means for absorbing said reflected one and other signal portions to eliminate said last-mentioned signal portions in said device.

2. A bilateral non-reflective transmission device as set forth in claim 1 which includes first frequency selective means connected in said first path for passing said one signal, and

second frequency selective means connected in said second path for passing said other signal,

and in which said first circuit means comprises a first branched circuit interconnecting said first input-output means and adjacent ends of said first and second paths for passing said one signal and reflected other signal portion in said given direction and said other signal in said opposite direction,

said second circuit means comprises a second branched circuit interconnecting said second input-output means and adjacent opposite ends of said first and second paths for passing said one signal in said given direction and said other signal and reflected one signal portion in said opposite direction,

and said absorbing means is coupled to said first and second branched circuits for absorbing said reflected one and other signal portions to eliminate said lastmentioned signal portions in said device.

3. A bilateral non-reflective transmission device as set forth in claim 1 which includes first frequency selective waveguide means connected in said first path for passing said one signal, and

second frequency selective waveguide means connected in said second path for passing said other signal, and in which said first and second signal paths comprise signal transmission waveguides,

said first circuit means comprises a first branched waveguide circuit having three ports of which one is connected to said first input-output means and second and third ports are connected to adjacent ends of said first and second waveguide paths, respectively, said one port passing said one signal and reflected other signal portion in said given direction and said other signal in said opposite direction, said second port passing said one signal and reflected other signal portion in said given direction, said first selective means reflecting said reflected other signal portion, and said third port passing said other signal in said opposite 9 direction and said reflected other signal portion in said given direction, said second circuit means comprises a second branched waveguide circuit having three ports of which one is pled to said last-mentioned fourth port and thereby to said first and second waveguide structures for absorbing said reflected one and other signal portions to eliminate said last-mentioned signal portions in said device.

C nn cted to said second input-output means d sec- 7. A bilateral non-reflective transmission device as set ond and third ports are connected t dj OPPoforth in claim 1 which includes a plurality of discrete site ends of said first and second waveguide paths, refrequently selective Waveguide means for Passing said spectively, said last-mentioned one port passing said other signal, and one signal in said given dire ti d id other i in which said first and second paths include signal transnal and reflected one signal portion in said opposite mission Waveguides, said seeorld Waveguide P r h direction, said last-mentioned second port passing Comprising tWo Parallel Waveguide branches, each said one signal in said given direction and said reincluding tWo of said frequency selective means flected one signal portion in said opposite direction, rleeted in spaced relation thereto, and said last-mentioned third port passing said other said first Circuit means comprising a first magic-tee signal and said reflected one signal portion in said having a first arm oormeeted to said first p p opposite direction, said second selective means remeans, second and third electrically equivalent arms flecting id fl t d one signal portion, connected to adjacent ends of said two parallel wave and said absorbing means is coupled to said first and guide branches, and a fourth arm Connected t an second three-port branched waveguide circuits for abend of said first Waveguide P adjacent to said lastsorbing said reflected one and other signal portions mentioned adlaeerlt two Parallel Waveguide braheh to eliminate said last-mentioned signal portions from ends, said first arm Passing said one and other id d i nals together with said reflected other signal portion, 4. A bilateral non-reflective transmission device as set said second and third arms Passing said other signal forth in claim 1 which includes first frequency selective together With said reflected other signal Portion and means connected in said first path for passing said one said fourth arm Passing said one signal, signal, and said second circuit means comprises a second magic-tee second frequency selective means connected in said sechaving a first arm connected to said second p d h f passing said other Signal, output means, second and third electrically equivaand in which said absorbing means comprises an lent arms connected to adjacent opposite ends of said lator connected in at least one of said first and second two Parallel Waveguide branches, and a fourth arm Paths between one f said fi t and second frequency connected to an opposite end of said first waveguide selective means and one of said first and second cirpath, said last-mentioned first arm passing said one cuit means, said isolator absorbing said reflected one e other signals together With said reflected 6 and other signals portions to eliminate said last-menslgnal P h said last-mentioned seeorld and third honed signal portions in Said device 3 arms passing said other signal, and said last-men- 5. A bilateral non-reflective transmission device as set tlcfned fourth arm Passing said one signal g r forth in claim 1 which includes first frequency selective wlthsald refleeted one signal P means connected in said first path for passing said one sald absorbmg means Comprising a p i y f signal, and 1solat=ors of which a first isolator is connected besecond frequency selective means connected in said sectween l two spaced frequency selective means n ond Path f passing id other signal, one of sa d two parallel waveguide branches, a second and in which Said absorbing means comprises a pluraL isolator 18 connected between said two spaced freity of isolators of which one isolator is connected quency selective means in the other of said tWO paralin said first path between said first frequency seleclet Waveguide branches, and a third at r is contive means and second circuit means and another isonected said first Waveguide P said rst a lator is connected in Said Second path between Said second isolators absorbing said reflected other signal Second frequency selective means and first circuit portion and sardthird isolator absorbing said reflected means, said one and other isolators absorbing said n Signal Portion to eliminate Said last-mentioned r fl t d one and other signal portions, respectively, reflected other and one signal portions in said device. to ehmihate said lasgmfihtiohed Signal portions in 8. A bilateral non-reflective transmission device as set said device forth in claim 1 which includes first and second wave- 6. A bilateral non-reflective transmission device as set guide filters connected in spaced relation i id fi t forth in claim 1 which includes first frequency selective path and passing said one signal, said second filter also waveguide means connected in said first path for passing p ssing said reflected one signal ortion, id o i al, d third and fourth waveguide filters connected in spaced second frequency selective Waveguide means connected relation in said second path and passing said other in said second path for passing said other signal, signal, said third filter also passing said reflected other and in which said first and second signal paths comprise signal portion,

signal transmission waveguides, each of said first, second, third and fourth filters insaid first circuit means comprises a first waveguide eluding .a plurality of interiorly spaced rods posistructure having three ports of which one port is tioned vertically on one wall in proximity of at least connected to said first input-output means and second one end thereof, and third ports are connected to adjacent ends of said and in which said first and second signal paths comprise first and second Waveguide paths, respectively, for 5 signal transmission waveguides, passing said one and other signals together with said said first circuit means comprises a first three-branch reflected other signal portion, rectangular waveguide circuit having a first branch said second circuit means comprises a second waveconnected to said first input-output means and secguide structure having four ports of which one port ond and third branches connected to adjacent ends is connected to said second input-output means and 7 of said first and second waveguide paths, respectivesecond and third ports are connected to adjacent 1y, for passing said one and other signals together opposite ends of said first and second paths, respecwith said reflected other signal portion, tively, and afourth port, said second circuit means comprises a second threeand said absorbing means comprises a dummy load coubranch rectangular circuit having a first branch connected to said second input-output means and second and third branches connected to adjacent opposite ends of said first and second waveguide paths, respectively, for passing said one and other signals together with said reflected one signal portion,

12 so as to substantially eliminate said reflected other signal portion, said first and second signal paths include signal transmission waveguides, said second waveguide path comprises two parallel waveguide said first filter so positioned in said first waveguide branches, each including one of said frequency selecpath as to space a first plane formed at a junction of tive Waveguide means, said first and second branches of said first waveguide said first circuit means comprising a first magic-tee circuit from said rods at said one end of said lasthaving a first arm connected to said first input-output mentioned filter at a distance which is approximately means, second and third electrically equivalent arms equal to an integral multiple of a half of the waveconnected to adjacent ends of said two parallel waveguide wavelength of a center frequency of said other guide branches, and a fourth arm connected to an signal in said second waveguide path to establish said e d of said first Waveguide path adjacent to said last-mentioned plane as a virtual surface for short l st-m ntioned adjacent two parallel waveguide circuiting said last-mentioned other signal together r nch ends, said first arm passing said one and other with said reflected other signal portion thereby re- 15 Signals, Said Second and third arms Passing Said other stricting the passing of said last-mentioned other sig- Signal, and Said fourth arrrl P g said one Signal, 1 d fl t d th i l ti t id Second said second circuit means comprising a second magic-tee waveguide path and first and third branches of said having a first arm Connected to Said Second p fi t Waveguide i i output means, second and third electrically equivalent said second filter so positioned in said first Waveguide arms oohheoted to adjacent pp ends of Said tWO path as to space a second plane formed at a junction Parethe1 Waveguide branches, and a fourth arm Collof said first and second branches of said second heoted to an pp end of Said first Waveguide waveguide circuit from said rods at said one end of Path, Said last-mentioned firSt arm Passing Said one said last-mentioned filter at a distance which is apand other Signals together With Said reflected n proximately equal to an integral multiple of a half Signal Portion, Said last-mentioned nd and third of the waveguide wavelength of a center frequency arms Passing Said other Signal, and i -m of said other signal in said second waveguide path ttohed fourth arm Passing Said one Signal together to establish said last-mentioned second plane as a vir- With said one Signal P tual surface for short circuiting said last-menitoned and, Said absorbing means p ng an is lat r conother signal thereby restricting the passing of said hected in Said one guid path for absorbing th i l to id second waveguide path and fi t said reflected one signal portion to eliminate said and third branches of said second waveguide circuit, lastmehtiohed Signal Portion irl Said i id thi d filt so pgsitioned i said second Waveguide 10. A bilateral reflective transmission device as set h as to Space a third plane formed at a junction of forth in claim 1 which includes first and second Wavesaid first and third branches of said first waveguide guide filters connected in spaced relation in said first path i i from id rods at Said one end f said last for passing said one signal, said second filter also passing mentioned filter at a distance which is equal approxi- 531d reflected one Signal P mately to an integral number of a half of the Wave a third waveguide filter connected in said second path guide wavelength of a center frequency of said one for Passing Said other Signal, signal i id fi t M/aveguide path to establish said each of said first and second waveguide filters includlast-mentioned third plane as a virtual surface for mg plurality of ihteriorly Spaced Pods P siti n d short circuiting said one signal thereby restricting Vertlcany oh one Well in Proximity of at least One the passing of said last-mentioned one signal to said f thereof, Said third filter including a pl rality f fi t Waveguide path and fi t and second branches interiorly spaced rods positioned vertically on one of said first Waveguide circuit, e In Phoxhhity of pp ends thereof,

said fourth filter so positioned in said second waveguide and In Which Said inherent impedance mismatch of Said h as to space a f th plane formed at a junction first input-output means is substantially minimized so f said fi t and third branches of said second Wave as to substantially eliminate said reflected other sigguide circuit from said rods at said one end of said i Said first and Second Signal Paths last-mentioned filter at a distance which is equal .pnse slghal transmission Waveguides, approximately to an integral multiple of a half of said first circuit means comprising a first three-branch h Waveguide Wavelength of a Center frequency of rectangular waveguide circuit having a first branch id one signal in said fi t Waveguide path to connected to said first input-output means and second bli said 1a t ti d fourth plane as a virtual and third branches connected to adjacent ends of said surface for short circuiting said one signal thereby refirst.and iecond Waveguidfi Paths respectively for stn'cting the passing of said last-mentioned one sig- Passmg 531d one and other Signals, naj and Said fl t d one signal portion to said said second circuit means comprising a second threefi t Waveguide path and first and second branches branch rectangular waveguide circuit having a first of id Second Waveguide circuit, branch connected to said second input-output means d id absorbing means Comprising a plurality of and second and third branches connected to adjacent isolators of which a first isolator is connected beopposlte ends of said first and Second Waveguide tween said first and second filters in said first wave- P respectively for Passing said one and other guide path to absorb said reflected one signal portion signals together with said reflected one signal pOrpassing through said second filter and a second isolator is connected between Said third and fourth said first filter so positioned in said first waveguide path filters in said second waveguide path to absorb said as to space a first Plane formed at a junction of said reflected oth i l portion passing through Said first and second branches of said first waveguide cirthird filter for eliminating said last-mentioned one Quit from Said rods at Said ne end of said last-menand pther signal portions in said device tioned filter at a distance which is approximately 9. bilateral nonreflective transmission device as set equal to an integral multiple of a half of the Waveioe ghle rr cfzgllacvlvhgh includes a plurality of discrete guide wavelength of a center frequency of said th aveguide means for passing sa d signal in said second waveguide path to establish ()flgerdsjgnaifs h i said last-mentioned first plane as a virtual surface nfi 1:15;:-giiilii hgllslslrglfiiigfe mismatch at said for short circuiting said last-mentioned other signal antially minimized thereby restricting the transmission of said other si nal to said second waveguide path and first and third branches of said first waveguide circuit,

said second filter so positioned in said first waveguide path as to space a second plane formed at a junction connected to an opposite end of said first waveguide path, said last-mentioned first arm passing said one and other signals, said last-mentioned second and third arms passing said other signal, said last-menof said first and second branches of said second tioned fourth arm passing aid one signal, waveguide circuit from said rods at said one end of d id absorbing means comprising a plurality of isoaid Ia t filter t a distance Whi h iS plators of which a first isolator is connected between PTOXimately equal t0 all integral multiple of half said first and second frequency selective waveguide of t e Waveg ide wavelength f a Center fr q n y means connected in one of said two parallel wave- Of said other Signal in Said Second waveguide p h guide branches and a second isolator is connected to establish said last-mentioned second plane as a b tw id third and fourth frequency selective virtual surface for short circuiting said last-mentioned waveguide means connected in the other of said two other signal thereby restricting the transmission of parallel waveguide branches, said first and second Said Other Signal to said Sewnd Waveguide P and isolators absorbing said reflected other signal portion first and third branches of said second waveguide 15 passing through said first and third frequency selec- Circuit, tive waveguide means for eliminating said last-mensaid third filter so positioned in said second waveguide tioned signal portion in said device- Pa as to spa third and f urth p s f m a 12. A bilateral reflective transmission device as set junctions of said first and third branches of said forth i claim 1 which includes first and Second Waveguide Circuits, respectively, from a first waveguide filter connected in said first path said rods at said opposite ends of said last-mentioned for passing said one signal, said first filter including filter at distances which are individually equal apa plurality of interiorly spaced rods positioned verproximately to an integral multiple of a half of the tically on one wall in proximity of opposite ends waveguide wavelength of a center frequency of said thereof, one signal in said first waveguide path to establish 5 second and third waveguide filters connected in spaced said last-mentioned third and fourth planes as virtual relation in said second path for passing said other surfaces for short circuiting said one signal and resignal, said second filter also passing said reflected flected one signal portion thereby restricting the other signal portion, each of said second and third transmission of said one signal and reflected one filters including a plurality of interiorly spaced rods signal portion to said first waveguide path and first positioned vertically on one wall in proximity of at and second branches of said first and second :waveleast one end thereof, guide circuits, and in which said inherent impedance mismatch of said and said absorbing means comprises an isolator consecond input-output means is substantially minimized nected between said first and second filters in said so as to substantially eliminate said reflected one first waveguide path for absorbing said reflected one signal portion, said first and second signal paths comsignal portion passing through said second filter to eliminate said last-mentioned one signal portion in said device.

11. A bilateral reflective transmission system as set prise signal transmission waveguide,

said first circuit means comprising a first three-branch waveguide circuit having a first branch connected to said first input-output means and second and third forth in claim 1 which includes a plurality of discrete frequency selective waveguide means for passing said other signal,

branches connected to adjacent ends of said first and second Waveguide paths, respectively, for passing said one and other signals together with said reflected other signal portion,

said second circuit means comprising a second threebranch Waveguide circuit having a first branch connected to said second input-output means and second and third branches connected to adjacent opposite ends of said first and second waveguide paths, respectively, for passing said one and other signals,

said first filter so positioned in said first waveguide path as to space first and second planes formed at junctions of said first and second branches of said first and second waveguide circuits, respectively, from said rods at said opposite ends of said last-mentioned frequency selective waveguide means passing aid filter at distances which are individually equal apother signal together with said reflected other signal proximately to an integral multiple of a half of the portion, waveguide wavelength of a center frequency of said said first circuit means comprising a first magic-tee Other Signal in Said Sewnd Waveguide P to having a first arm connected to said first input-output t-ablish said last-mentioned first and second planes means, second and third electrically equivalent arms as virtual surfaces for short circuiting said other sigconnected to adjacent ends of said two parallel wavenal and reflected other signal portion thereby reguide branches, and a fourth arm connected to an stricting the transmission of said other signal and end of said first waveguide path adjacent to said lastreflected other signal portion to said second wavementioned adjacent two parallel waveguide branch guide path and first and third branches of said first ends, said first arm passing said one and other sigand second waveguide circuits, nals together with said reflected other signal portion, said second waveguide filter so positioned in said secsaid signal and third arms passing said other signal 011d waveguide path as to space a third plane formed together with said reflected other signal portion, and at a junction of said first and third branches of said said fourth arm passing said one signal, first waveguide circuit from said rods at said one end said second circuit means comprising a second magicof said last-mentioned filter at a distance which is tee having a first arm connected to said second inputequal approximately to an integral multiple of a half output means, second and third electrically equivaof the waveguide wavelength of a center frequency lent arms connected to adjacent opposite ends of said of said one signal in said first Waveguide path to two parallel waveguide branches, and a fourth arm establish said last-mentioned third plane as a virtual surface for short circuiting said one signal thereby and said absorbing means comprises an isolator conrestricting the transmission of said last-mentioned et d between said second and third filters in said one Signal to Said first Waveguide P and first and second waveguide path for absorbing said reflected Second branches of Said first Waveguide Circuit, other signal portion passing through said second said third waveguide filter so positioned in said second 5 filt to eliminate Said last mentioned Signal portion waveguide path as to space a fourth plane formed in said device at a junction of said first and third branches of said second waveguide circuit from said rods at said one References Cited end of said last-mentioned filter at a distance which UNITED STATES PATENTS is equal approximately to an integral multiple of a 10 half of the waveguide wavelength of a center fre- 1,481,831 1/1924 Demarest 17915 quency of said one signal in said first waveguide path 2,702,371 2/1955 su t i 333 73 to establish said last-mentioned fourth plane as a 95 7 3 5 1 Tinotson 3 virtual surface for short circuiting said one signal thereby restricting the transmission of said 1ast-mer1- l5 HERMAN KARL SAALBACH, Primm-y Examinen tioned one signal to said first waveguide path and first and second branches of said second waveguide GENSLER, Assistant Examine"- circuit, 

1. A BILATERAL NON-REFLECTIVE TRANSMISSION DEVICE FOR PASSING ONE AND OTHER ELECTROMAGNETIC SIGNALS OCCUPYING DIFFERENT FREQUENCY BANDS IN OPPOSITE DIRECTIONS COMPRISING: FIRST INPUT-OUTPUT MEANS HAVING AN INHERENT IMPEDANCE MISMATCH FOR SAID OTHER SIGNAL AND PASSING SAID ONE AND OTHER SIGNALS AND REFLECTING A PORTION OF SAID OTHER SIGNAL, SECOND INPUT-OUTPUT MEANS HAVING AN INHERENT IMPEDANCE MISMATCH FOR SAID ONE SIGNAL AND PASSING SAID ONE AND OTHER SIGNALS AND REFLECTING A PORTION OF SAID ONE SIGNAL, A FIRST PATH TRANSMITTING SAID ONE SIGNAL IN A GIVEN DIRECTION FROM SAID FIRST INPUT-OUTPUT MEANS TO SAID SECOND INPUT-OUTPUT MEANS TO SAID SECOND INPUT-OUTPUT MEANS, A SECOND PATH TRANSMITTING SAID OTHER SIGNAL IN A DIRECTION OPPOSITE TO SAID GIVEN DIRECTION FROM SAID SECOND INPUT-OUTPUT MEANS TO SAID FIRST INPUT-OUTPUT MEANS, FIRST CIRCUIT MEANS INTERCONNECTING SAID FIRST INPUT-OUTPUT MEANS AND ADJACENT ENDS OF SAID FIRST AND SECOND PATHS FOR PASSING SAID ONE SIGNAL AND REFLECTED OTHER SIGNAL PORTION IN SAID GIVEN DIRECTION AND SAID OTHER SIGNAL IN SAID OPPOSITE DIRECTION, SECOND CIRCUIT MEANS INTERCONNECTING SAID SECOND INPUTOUTPUT MEANS AND ADJACENT OPPOSITE ENDS OF SAID FIRST AND SECOND PATHS FOR PASSING SAID ONE SIGNAL IN SAID GIVEN DIRECTION AND SAID OTHER SIGNAL AND REFLECTED ONE SIGNAL PORTION IN SAID OPPOSITE DIRECTION, AND MEANS COUPLED TO SAID FIRST AND SECOND CIRCUIT MEANS FOR ABSORBING SAID REFLECTED ONE AND OTHER SIGNAL PORTIONS TO ELIMINATE SAID LAST-MENTIONED SIGNAL PORTIONS IN SAID DEVICE. 